Vehicle manufacturers are implementing lighter, stronger materials, such as aluminum alloys to meet emission reduction goals, meet fuel economy goals, reduce manufacturing costs, and reduce vehicle weight. Increasingly demanding safety standards must be met while reducing vehicle weight. One approach to meeting these competing interests and objectives is to hydro-form high strength aluminum alloy tubular blanks into strong, lightweight hydro-formed parts.
Aluminum tube types include seam-welded tube, extruded seamless tube, and extruded structural tube. Seam-welded tube and extruded seamless tube are expensive. Seam-welded tubes and extruded seamless tubes are expensive to convert to finished hydro-formed parts. Extruded structural tubes are lower in cost because they are formed in a continuous mill operation having a greater line and material utilization efficiency than extruded seamless tubes and seam-welded tubes.
Extruded structural tubes are formed by extruding an aluminum billet through an extrusion die at a high temperature and at high pressure. Discontinuous material flow across the section of the shape occurs when the flowing aluminum separates in the mandrel plate and re-converges in the cap section. A weld line, or joining line, is created where the flowing aluminum re-converges to form the extruded shape. Extruded structural tubes may have two or more weld lines that are an artifact of the porthole extrusion process.
Hydro-forming complex parts may require a series of bending, pre-forming, hydro-forming, piercing and machining operations. Bending and hydro-forming aluminum tubes is not currently in use in high volume production operations. (ie. more than 100,000 units/year) Aluminum intensive vehicles (AIVs) are envisioned that use metal forming methods consistent with current conventional automotive manufacturing methods.
In a high pressure hydro-forming (HPH) operation, the tube is inserted in the HPH die before any fluid under pressure is provided inside the tube. The dies are closed that can result in buckling the tube's cross-section. High pressure incompressible hydro-forming fluid, such as water, is supplied to expand and shape the tube to conform to the die cavity. Substantial press tonnage is required to hydro-form parts in HPH processes. Substantial expansion of the tube (circumferential length of line expansion of more than 5%) is necessary to eliminate any tube buckles and produce complexly shaped parts. It is not feasible to form most parts from aluminum tubes with high expansion HPH operations because aluminum seam-welded, seamless tubes and structural extrusion tubes are less formable than mild steel tubes.
The above challenges and other challenges are addressed by this disclosure as summarized below.